Combustion zone control



June 24, 1958 v. z. CARACRISTI COMBUSTION ZONE CONTROL Fiied Jan! 16,1953 2 Sheets-Sheet 1 Steam to Turbine R o T N E V m r IH. 2H 4 9 a F w2 u l m m m m 2 mmmm mwwm p O U L Virginius Z. Coracristi WM ATTORNEIY 2Sheets-Sheet 2 Filed Jan. 16, 1953 Upper Firing Olrcle IntermediateFiring Circle Lower Firing Circle Fig.

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coMnUsTIoN zoNE CONTROL Virginius Z. Caracristi, Bronxville, N. Y.,assignor to Combustion Engineering, Inc., New York, N. Y., a corporationof Delaware Application January 16, 1953, Serial No. 331,605

' 2 Claims. Cl. 122478) This invention relates to an improvement in theregulation of the temperature of the steam leaving the superheater of asteam generator. It is particularly applicable. to a superheater solocated in a boiler that substantially all the heating effect is byconvection from the products of combustion leaving the furnace whosewalls are lined with water coo-led surfaces and in which turbulent fuelfiring is employed.

It is well known that in the operation of such a steam generating unitthe temperature of the superheated steam varies with fluctuations insteam output; a reduction in superheated steam temperature occurringwith a reduction in rating. Because it is undesirable to furnish steamof different temperature to the turbine various means have been devisedto correct for steam temperature fiuctuations.

One method of regulating the temperature of the superheated steam is tocause variation in heat absorption within the furnace from the fuelburned therein so that the gases passing over the superheated surfaceare at a temperature capable of producing the desired degree ofsuperheat. A method of this nature is disclosed in the patent toKreisinger et al., No. 2,363,875 of November 28, 1944.

This method provides for directing streams of fuel and air tangentiallytowards the periphery of an imaginary cylinder generally co-axial withthe furnace chamber, and for tilting the streams of fuel and airupwardly towards the furnace chamber outlet or downwardly away from thefurnace chamber outlet. A variation in heat absorption by the furnaceheating surface is thereby obtained. 4 This results in a higher or lowertemperature of the gases leaving the furnace and consequently a higheror lower superheat depending on whether the burners are tilted upwardlyor downwardly. At any given tilting position the streams of fuel and airissuing from the burner D nozzles are tangentially directed towards animaginary horizontal firing circle the diameter of which is heldconstant.

In theroperation of steam generators of this type it has been found thatwith burners as presently designed, a tilt downwardly from thehorizontal will not cause as much variation in gas temperature as a tiltof equal angularity when directed upwardly from the horizontal.Consequently the controlled superheated steam temperature is eifectedconsiderably more by tilting the burners upwardly than when tilting theburners downwardly an equal angular degree.

It is an important object of this invention to overcome the abovedisadvantage and to make the tilting of tangentially fired burnersdownwardly equally as effective as the tilting of these burnersupwardly.

Furthermore, I have found that the effect of burner tilt upon thetemperature of the gases and consequently upon the temperature of thesuperheated steam can be increased by a reduction in firing circlediameter when States Patent 2 tilting upwardly, and by an increase infiring circle diameter when tilting downwardly.

Accordingly another important object of my invention is to increase thesteam temperature control range considerably by an appropriate andgradual change in the diameter of the firing circle from a relativelysmall diameter at the maximum upward tilt position to a relatively largediameter circle at the maximum downward tilt position of the burners.

Additional objects and advantages will become apparent from thefollowing description of an illustrative embodiment of the inventionwhen read in conjunction with the accompanying drawings wherein:

Figure l is a schematic side view of a steam generator illustrating apreferred application of the invention.

Figure 2 is a horizontal schematic plan view taken on line 22 of Fig. 1.

Figure 3 is a simplified elevational view of a burner unit taken on line3-3 of Fig. 2 showing one application of my invention to a set ofburners tilted with respect to the vertical axis of the furnace chamber.

Figure 4 is a set of curves which illustrate graphically how theapplication of my invention extends the steam temperature control range.

In Figure 1 the boiler illustrated includes a steam and water drum 10.This drum supplies water through the downcomers 12 to the lower waterwall headers 14, 16 and 18 to which are connected the lower ends ofwater cooled tubes 20 forming the walls and roof of the furnace chamber22. The upper ends of some of the aforesaid water cooled furnace tubes20 are connecteddirectly to steam and water drum 10. Others terminate inupper water wall header 24 which in turncommum'c'ates with drum 10through connecting tubes 26. In the lower portion of the furnace chambertangentially firing burners 28 are arranged in each corner such as shownin Fig. 2. In the illustrative embodiment shown each of these burners isequipped with three fuel and air ports 28a, 28b, and 28c. Fuel and airis discharged through each of these ports into the furnace in adirection along a line which is tangential to the periphery of animaginary firing circle. The combustion gases follow a spiral flow pathupwardly towards the furnace outlet 29, while giving off a substantialportion of the heat contained in the gases to the water wall tubes 20for steam generation. In leaving the furnace the gases enter a generallyhorizontal gas pass 30 in which are suspended a high temperaturesuperheater section 31 and a low temperature superheater section 32. Avertical gas pass 34 extends downwardly from the rear portion of saidhorizontal passage 30. Additional heat absorbing surfaces such aseconomizer 36 or air heater surface (not shown) may be arranged in gaspass 34 through which the gases flow on their way to a stack (notshown).

The steam generated in water wall tubes 20 enters drum 10 together witha certain amount of recirculated water. The steam is separated from thewater by suitable apparatus located within the steam and water drum 10and the separated dry saturated steam enters superheater inlet header 38via superheater connecting tubes 40. In passing through low temperaturesection 32 and high temperature section 31 heat is applied to thesaturated steam and its temperature raised to a desire-d degree ofsuperheat. The superheated steam thereupon leaves high temperaturesection 31 through outlet header 42 and is conveyed to a steam turbine(not shown) by steam pipe 44.

In operation it frequently becomes necessary to change the steamcapacity of the unit. The superheated steam temperature generally varieswith the amount of steam generated by the unit. Other operatingconditions such as slagging-over of furnace heating surface may alsoaffeet the superheated steam temperature. .In orderto operate theturbine at maximum efficiency it is most desirable to supply the turbinewith superheated steam of a constant temperature regardless of-steamload' or other varying operating conditions. :As' pointed out earlierherein one method of controlling and maintaining a constant superheatedsteam temperature regardless of variations in steam generator capacity,providesfor changing the heat absorbed by the-water walls by alteringthe location of the combustion zone within the furnace. The temperatureof the gases leaving the furnace is thereby controlled and accordinglythe degree ofsupcrheat.

. Although this method when applied to a modern steam generatorgenerally solves the problem caused by variations in steam temperaturewith change in steam load it has been found that the effect oftemperature change when tilting the burners upwardly a given angulardegree far exceeds that when tilting the burners downwardly an equalangular degree when firing tangentially towards a firing circle ofrelatively small diameter. In other words, under. these conditions adownward tilt is considerably less effective in changing the superheatedsteam temperature than an upward tilt of equal angularity. l

In attempting to overcome the above difficulties it wasfound that asubstantial equality in effectiveness of temperature change may beobtained by increasing 'the diameter of the firing circle. However, aportion of the steam temperature control range must thereby be sacrificed. A still further increase in firing circle diameter revealed thata downward tilt under these conditions may become more effective inchanging the steam temperaturethgin an upward tilt of equal angularity.

To overcome the above difficulty I have made use of the fact that theeffectiveness of burner tilting upon the steam temperature can beincreased both by a reduction in firing circle diameter when tiltingupwardly, and by an increase in firing circle diameter when tiltingdownwardly. Accordingly, my method and apparatus as disclosed herein forfiring fuel tangentially, provides for a gradual decreasegof the firingcirclewhen tilting burners upwardly and a gradual increase of the firingcircle when tilting the burners downwardly.

By varying the firing circle diameter inthis manner in a steam generatorequipped with my inventive improvement it is therefore possibleto obtaina' substantially equal increaseand decrease in, steam temperature withtilting angles of substantially equal degree upwardly or downwardly fromthe horizontal. Furthermore, and this is even more important, thecontrol of the superheated steam temperature is extended over a widerload range of the steam generator.

This is graphically illustrated in Fig. 4. There steam temperaturevariations are plotted against various angles of vertical burner tiltover a tilting range extending from minus degrees (downwardly) to plus30 degrees (upwardly) from the horizontal. This is indicated by curvesX, Y and Z. Curve X represents temperature variations plotted forvarious angles 'of burner tilt-upwardly and downwardly from thehorizontal-when firing tangentially towards a fixed and relatively smallfiring circle such as of 2 feet diameter. Curve Y represents temperaturevariations plotted for various angles of burner tilt upwardly anddownwardly from the horizontalwhen firing tangentially towardsia fixedand relatively large firing circle such as of 6 feet diameter. a

It will be noted thatcurve X (small diameter firing circle) drops fromthe horizontal-burner position e to the lowermost 30 degree position aand rises from the horizontal position e to the uppermost 30 degreeposition b. In a similar manner 'cur ve Y (large diameter firing circle)drops from a horizontal position g to a lowermost position 0 and risesfrom the horizontal position g to the uppermost position d. i a i I Itwill further be noted that the temperature variation 4 (e-b) obtained byan upward tilt when usinga small firing circle as indicated by curve Xsubstantially exceeds that (e-a) obtained by a downward tilt with thesame small firing circle. Conversely the temperature variation (g-a')obtained by an upward tilt when using a large firing circle as indicatedby curve Y is considerably less in extent than that (gc) obtained by adownward tilt when directed tangentially at the same large firingcircle.

My inventive improvement in burner tilting as herein disclosed takesadvantage of the inequalities in temperature variation so clearly shownby curves X and Y. This is accomplished by varying the diameter of thefiring circle from a relatively small diameter such as two feet at themaximum upward tilt to a relatively large diameter such as 6 feet at thelowermost downward tilt position.

Thus, in a steam generator equipped with my invention, the temperaturevariations when plotted against the angle of burner tilt will follow aline represented by curve Z. The uppermost point I) of curve Z is commonwith curve X indicating that in the uppermost tilting position (+30) :1small firing circle diameter is utilized. The lowest point 0 of curve Zis common with curveY indicating that in the lowermost tilting position(-30) a large firing circle is utilized.

It will also be noted that when gradually increasing the firing circlediameter (from 2 feet to 6 feet for instance) as represented by curve Zthe temperature variation (hb) between the horizontal position 12 andthe uppermost position b approximately equals the temperature variationh-cbetween position I1 and lowermost tilting position 0. 7

Furthermore, it will be noted by studying Fig. 4 that when employing myimproved burner tilting method and apparatus in the water cooled furnaceof a steam generator having superheater heating surface absorbing heatprimarily by convection, the burner tilting effect upon the steamtemperature is substantially increased over that obtainable when usingeither a small or large but fixed firing circle diameter. This isclearly demonstrated by comparing the overall temperature variation (0to b) of curve Z (using variable firing circle) with the temperaturevariations (a to b) of curve X or (c to d) of curve Y, both based on afixed firing circle diameter.

Thus my invention provides that the set of burners and air nozzles 28 inthe furnace chamber be mounted so that tilting of each discharge port28a, 28b, and 28c occurs individually about respective axes Ta, Tb, andTc each of which forms an angle A with the horizontal H, asschematically illustrated in Figure 3. When discharging fuel and airthrough these ports in a horizontal direction they are set so that thesestreams of fuel and air are directed tangentially at the periphery ofintermediate firing circle I. The angle A between the tilting axes Ta,Tb and Tc of the burners and of the horizontal H is such that whenthe'fuel and air streams are directed upwardly they will follow a linetangent to the periphery of an upper firing circle U which is smallerthan the aforementioned intermediate firing circle I. In dischargingfuel and air streams through these burners downwardly said streams willflow in a direction tangential to the periphery of a lower firing circleL which will be correspondingly larger than the intermediate firingcircle I. Angle A is preferably of a magnitude which results in an upperfiring circle diameter of about two feet and a lower firing circlediameter of about six feet, when the burners are tilted upwardlyordownwardly approximately 30 degrees. Obviously, angle A may vary withthe geometrical shape of the furnace chamber, with the arrangement ofwater wall heating surface, or may be affected by other factors such asgas new set of operating conditions that may be encountered such aschange in fuel and change in slagging conditions of the furnace walls.

A burner designed according to my invention and operating as hereinafterset forth will therefore in the preferred embodiment illustrateddischarge fuel and air tangentially towards the periphery of a frustumof a circular cone having a lower base formed by lower firing circle Land an upper base formed by the upper firing circle U. The plane withinwhich the tilting of the burner nozzles occurs would be the tangentplane which touches the conical surface of the imaginary frustum. Thisis schematically illustrated in Fig. 1.

Although I have described herein a preferred embodiment of my inventionwherein the burners are tilted to follow the outline of an imaginaryconical surface, my invention is also applicable to the tilting ofburners following an irregular or curved outline such as the periphcryof any solid of rotation located within the furnace chamber.

Furthermore, although in my preferred embodiment as herein described theimaginary frustum of a cone is coaxial with the furnace chamber, myinvention is not restricted thereto but could also be practiced in anorganiza-' tion wherein the axis of the imaginary solid of rotation(such as the frustum of a cone) is neither coinciding with nor parallelto the longitudinal axis of the furnace. The shape of the furnacechamber, the arrangement of the water wall heating surface or otherheating surfaces located therein may be such as to dictate the form andaxial location of the imaginary solid of rotation by which the tiltingof the burner nozzles is guided for the control of the temperature ofsuperheated steam.

Furthermore my improved tilting burner superheat control means can beemployed in combination with, or can be supplemented by other superheatcontrol means such as bypass damper control, desuperheating control orgas recirculation control.

In Fig. 3 of the illustrative embodiment of my invention three burnernozzles such as 28a, 28b and 280 are shown to constitute'one set ofburner nozzles in each corner. To accomplish the object of my inventionthe axis SS of the entire set of burner nozzles is tilted from thevertical V. Other means of tilting could be employed to achieve theobject of my invention such as tilting each individual burner nozzleindependently of all the others and following its own imaginary outlinelocated within the furnace such as the conical surface of a frustum orthe surface of any other solid of rotation.

.Such a furnace may be placed in any position, upright or horizontal andthe above described imaginary solid of rotation may have the shape of anhourglass or may be composed of two frustums joined end to end with thesmaller base in common.

I claim:

1. In a steam generator having an elongated furnace chamber equippedwith water cooled walls and an outlet for the furnace gases at one endthereof; a superheater for superheating steam located adjacent saidfurnace outlet in position to absorb heat from said gases; at least twoburner nozzles oppositely mounted in said furnace walls each firing afluid fuel in directions tangential to an imag inary firing circlelocated within said furnace chamber; means for mounting said burnernozzles for tilting in an are extending from an uppermost burner tiltposition to a lowermost burner tilt position for increasing ordecreasing the temperature of said superheated steam when tilt-.

ing said burner nozzles upwardly or downwardly respectively; said meansincluding a pivotally supported axis for tilting each nozzle in anarcfalling in a plane located at one side of the longitudinal axis ofsaid furnace and inclined in a direction toward said furnace axis at thefurnace outlet side of said burner nozzles, whereby said firing circledecreases gradually in diameter as the burner nozzle is tilted towardthe furnace outlet end from the lowermost position to the uppermostposition thereof.

2. An organization as defined in claim 1 wherein said firing circledecreases gradually to a diameter of approximately one half, whentilting the burner nozzles 30 degrees upwardly from the horizontal, ascompared to the firing circle that prevails when tilting the burnernozzles downwardly 30 degrees from the horizontal.

References Cited in the file of this patent UNITED STATES PATENTS2,243,909 Kruger June 3, 1941 2,363,875 Kreisinger et a1 Nov. 28, 19442,575,885 Mittendorf Nov. 20, 1951 2,590,712 Lacerenza Mar. 25, 1952

